Fun : Example Refactor of PrimeGenerator

initial.java

// Code from article here : https://qntm.org/clean
package literatePrimes;

import java.util.ArrayList;

public class PrimeGenerator {
private static int[] primes;
private static ArrayList<Integer> multiplesOfPrimeFactors;

  protected static int[] generate(int n) {
  primes = new int[n];
  multiplesOfPrimeFactors = new ArrayList<Integer>();
    set2AsFirstPrime();
    checkOddNumbersForSubsequentPrimes();
    return primes;
    }

    private static void set2AsFirstPrime() {
    primes[0] = 2;
    multiplesOfPrimeFactors.add(2);
    }

    private static void checkOddNumbersForSubsequentPrimes() {
    int primeIndex = 1;
    for (int candidate = 3;
    primeIndex < primes.length;
    candidate += 2) {
    if (isPrime(candidate))
    primes[primeIndex++] = candidate;
    }
    }

    private static boolean isPrime(int candidate) {
    if (isLeastRelevantMultipleOfNextLargerPrimeFactor(candidate)) {
    multiplesOfPrimeFactors.add(candidate);
    return false;
    }
    return isNotMultipleOfAnyPreviousPrimeFactor(candidate);
    }

    private static boolean
    isLeastRelevantMultipleOfNextLargerPrimeFactor(int candidate) {
    int nextLargerPrimeFactor = primes[multiplesOfPrimeFactors.size()];
    int leastRelevantMultiple = nextLargerPrimeFactor * nextLargerPrimeFactor;
    return candidate == leastRelevantMultiple;
    }

    private static boolean
    isNotMultipleOfAnyPreviousPrimeFactor(int candidate) {
    for (int n = 1; n < multiplesOfPrimeFactors.size(); n++) {
    if (isMultipleOfNthPrimeFactor(candidate, n))
    return false;
    }
    return true;
    }

    private static boolean
    isMultipleOfNthPrimeFactor(int candidate, int n) {
    return
    candidate == smallestOddNthMultipleNotLessThanCandidate(candidate, n);
    }

    private static int
    smallestOddNthMultipleNotLessThanCandidate(int candidate, int n) {
    int multiple = multiplesOfPrimeFactors.get(n);
    while (multiple < candidate)
    multiple += 2 * primes[n];
    multiplesOfPrimeFactors.set(n, multiple);
    return multiple;
    }
    }

revision.java

package literatePrimes;

import java.util.ArrayList;

public class PrimeGenerator {
  private static int[] primes;
  private static ArrayList<Integer> multiplesOfPrimeFactors;

  protected static int[] generate(int n) {
    primes = new int[n];
    multiplesOfPrimeFactors = new ArrayList<Integer>();

    // Set 2 as First Prime
    primes[0] = 2;
    multiplesOfPrimeFactors.add(2);

    _attachSubsequentPrimes();

    return primes;
  }

  private static void _attachSubsequentPrimes() {
    int primeIndex = 1;

    for (int candidate = 3;primeIndex < primes.length;candidate += 2) {
      if ( !isPrime( candidate ) )
        continue;

      primes[primeIndex++] = candidate;
    }
  }

  private static boolean isPrime(int candidate) {
    if (isLeastRelevantMultipleOfNextLargerPrimeFactor(candidate)) {
      multiplesOfPrimeFactors.add(candidate);
      return false;
    }

    return ( isMultipleOfAttachedPrimeFactors(candidate) ? false : true );
  }

  private static boolean isLeastRelevantMultipleOfNextLargerPrimeFactor(int candidate) {
    int nextLargerPrimeFactor = primes[multiplesOfPrimeFactors.size()];
    int leastRelevantMultiple = nextLargerPrimeFactor * nextLargerPrimeFactor;
    return candidate == leastRelevantMultiple;
  }

  private static boolean isMultipleOfAttachedPrimeFactors(int candidate) {
    for (int n = 1; n < multiplesOfPrimeFactors.size(); n++) {
      if ( candidate != smallestOddNthMultipleNotLessThanCandidate(candidate, n) )
        continue;
    
      return true;
    }

    return false;
  }

  private static int smallestOddNthMultipleNotLessThanCandidate(int candidate, int n) {
    int multiple = multiplesOfPrimeFactors.get(n);

    while (multiple < candidate)
      multiple += 2 * primes[n];

    multiplesOfPrimeFactors.set(n, multiple);

    return multiple;
  }

}

Here's my take at a revision: https://github.com/marcospedreiro/prime-numbers/blob/master/src/main/java/org/example/prime_numbers/PrimeNumbers.java